The most challenging problem faced by the perfumery industry lies in the degradation and relatively rapid loss of the olfactive benefit provided by odoriferous compounds due respectively to their chemical structure and volatility, particularly that of “top-notes”. In addition, perfume perception needs to be provided at the right moments during the application of perfumed consumer goods while ensuring perfume optimal impact. These problems are generally tackled using a delivery system, e.g. microcapsules containing a perfume, to protect and to release the fragrance in a controlled manner.
Over the past two decades, different types of core-shell microcapsules have been developed and disclosed in the prior art. Polymeric materials such as melamine-formaldehyde as those described for example in U.S. Pat. No. 4,260,515, U.S. Pat. No. 4,898,696, or WO2006131846, and polyurea described for example in US20020064654, WO2009153695 or WO2011154893, have been used to make the microcapsule membranes. In these cases, the microcapsule shell is either the product of a polycondensation process of a polymeric resin from the aqueous phase, or in the case of polyurea, the product of an interfacial polymerisation reaction between a polyisocyanate, soluble in the core, and a polyamine that is water soluble. The functionalisation and modification of these capsules are also well known and described for instance in WO2008098387 or in WO2012107323. Despite their performance in term of long-lastingness for particular perfume compositions and in specific applications, these microcapsules would still need to be further improved. In particular, the presence of residual monomers but also the limited storage stability of capsules in application or yet the restriction in term of perfume creation are limiting factors that compromise the business growth of these microcapsules. On the other hand the mechanical properties of core/shell microcapsules are important for their ability to deliver active ingredients. In particular, for capsules intended to release their load upon rubbing, the resistance of the capsule shell against mechanical forces is a key property. The desirable barrier properties of core/shell microcapsules formulated for optimum stabilization of the active ingredient are also linked to the mechanical properties of the capsules. Consequently, a common problem is that stable microcapsules may be optimized for stability, but they are mechanically too robust to be broken during the final application (such as the rubbing of a textile or skin). Therefore, it would be desirable to prepare microcapsules that exhibit mechanical properties such that they can easily be broken during the final application to release the active ingredient in a burst.
More recently, different approaches have been disclosed to improve core-shell microcapsules by developing formaldehyde-free aminoplast-based microcapsules as described in WO2013068255. Also, functional monomers have been introduced in polyurea membrane. For instance WO2009147119 discloses hybrid microcapsules wherein amino functionalized silane is reacted with polyisocyanates to form a hybrid capsule membrane. The developments in this area have also been using materials that are based on other silane compounds. In this regard, silane monomers such as tetraethoxysilane (TEOS), their analogues and functionalized versions have been largely described for use in the preparation of inorganic microcapsules for the encapsulation of diverse active ingredients including sunscreen products, e.g. in U.S. Pat. No. 6,238,650; and perfumes e.g. in WO2009106318, WO2011124706, or yet in EP2500087. Although, these capsules can be produced with reduced content of residual monomers, their membrane is usually highly porous whatever the monomer content, therefore implying a poor retention of low molecular weight molecules such as perfumery raw materials. A recent approach disclosed in WO2013083760 consisted in adjusting the process parameters starting from the formation and condensation of a mixture of polysilicones that cross-link to consolidate the membrane structure. Nevertheless, the capsules there-obtained are not satisfying as they demonstrate poor perfume retention which compromises their use in perfumery applications.
Despite the solutions described heretofore, there is therefore still a need within the perfumery industry to design a new generation of microcapsules with a good perfume retention and improved stability over a large range of pH values, while controlling their mechanical properties, and avoiding the generation or the presence of residual monomers.
The present invention addresses the problems mentioned above with stable core-shell microcapsules having a wall made from the hydrolysis and condensation reaction of a particular polyalkoxysilane macro-monomeric composition. Said composition also object of the invention can be introduced or prepared in situ in the oil phase during the process of preparation of the microcapsules.